Patent Application
20130257442
1. Technical Field
The present disclosure relates to circuits and, particularly, to a power source detection circuit and an electronic device with the power source detection circuit.
2. Description of Related Art
Electronic devices, such as mobile phones, digital cameras, and electronic readers, can be powered by a battery or an external power source, such as a power adapter. When the electronic device is powered by the battery, there is need to display the remaining power of the battery usually, when the electronic device is powered by the power adapter, there is no need to display the remaining power of the power source. However, it is needed to provide a detection circuit to detect whether the electronic device is powered by a battery or the power adapter and to display the remaining power of the battery in case the battery is used.
However, the common detection circuit is complex. A new power source detection circuit and an electronic device with the power source detection circuit, to overcome the described limitations, is thus needed.
Many aspects of the present disclosure are better understood with reference to the following drawing. The components in the drawing are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawing, like reference numerals designate corresponding parts throughout the view.
The FIGURE is a circuit diagram of an electronic device with a power source detection, in accordance with an exemplary embodiment.
Embodiments of the present disclosure will be described with reference to the accompanying drawings.
The FIGURE illustrates an electronic device 100 of the embodiment. The electronic device 100 includes a power port 10, a power source detection circuit 20, and a processing unit 30.
The power port 10 is used to connect a power source 200. In the embodiment, the power source 200 can be a power adapter or a battery.
The power source detection circuit 20 includes a voltage conversion module 201 and a signal producing module 202. The voltage conversion module 201 is used to convert a voltage of the power source 200 connected to the power port 10 to a detection voltage. In the embodiment, the detection voltage is proportional to the voltage of the power source 200. The signal producing module 202 is connected to the voltage conversion module 201 and the processing unit 30, and is used to compare the detection voltage with a reference voltage. The signal producing module 202 produces a high voltage signal when determining the detection voltage is less than the reference voltage, and produces a low voltage signal when determining the detection voltage is greater than the reference voltage.
The processing unit 30 determines the power source 200 is a battery and controls to display the remaining power of the battery, when receiving the high voltage signal from the signal producing module 202. The processing unit 30 determines the power source 200 is a power adapter, and controls not to display the remaining power of the battery, when receiving the low voltage signal from the signal producing module 202.
In detail, the voltage conversion module 201 includes a first resistor R1 and a second resistor R2. The first resistor R1 and the second resistor R2 are connected between the power port 10 and ground in series. When the power port 10 is connected to the power source 200, the voltage of the power source 200 is divided by the first resistor R1 and the second resistor R2. A connection node N of the first resistor R1 and the second resistor R2 constitutes an output port of the voltage conversion module 201 and outputs the detection voltage accordingly. In the embodiment, the voltage of the second resistor R2 is the detection voltage.
The signal producing module 202 includes a positive-negative-positive bipolar junction transistor (pnp BJT) and a third resistor R3. An emitter of the pnp BJT Q1 is connected to a voltage port V3.3, a collector of the pnp BJT Q1 is grounded via the third resistor R3, a base of the pnp BJT Q1 is connected to the connection node N of the first resistor R1 and the second resistor R2. In another embodiment, the pnp BJT Q1 can be replaced by a P-channel metal-oxide-semiconductor field-effect transistor.
In the embodiment, the voltage port V3.3 provides the reference voltage. In more detail, the voltage port V3.3 is connected to a voltage regulator (not shown) which produces a constant reference voltage. The processing unit 30 includes a detection pin 301. The collector of the pnp BJT Q1 is also connected to the detection pin 301 of the processing unit 30.
In the embodiment, the resistance values of the first resistor R1 and the second R2 is preset to ensure the detection voltage is higher than the reference voltage when the power port 10 connects to the power adapter, and make the detection voltage lower than the reference voltage when the power port 10 connects to the battery. For example, as is known, the voltage of the power adapter is usual 12 volt (V), the voltage of the battery is usually 6V-8V. If the resistance value of the first resistor R1 is 130 ohm, the resistance value of the second resistor R2 is 51 ohm, and the reference voltage is 3.3 V, then when the power port 10 connects to the power adapter. The voltage of the connection node N, namely the conversion voltage is 12*51/(51+130)=3.38 V, which is higher than the reference voltage. When the power port 10 connects to the battery, the voltage of the connection node N, namely the conversion voltage is between 6*51/(51+130)=1.69 V to 8*51/(51+130)=2.254 V, which is lower than the reference voltage.
Therefore, when the power source 200 connected to the power port 10 is the power adapter, the voltage of the base of the pnp BJT Q1 is higher than the voltage of the emitter of the pnp BJT Q1, and then the pnp BJT Q1 is turned off accordingly. The collector of the pnp BJT Q1 is grounded via the third resistor R3 and is at a low voltage. The detection pin 301 of the processing unit 30 is connected to the collector of the pnp BJT Q1 and obtains the low voltage signal. The processing unit 30 then does not display the remaining power of the battery when receiving the low voltage signal.
When the power source 200 connected to the power port 10 is the battery, the voltage of the base of the pnp BJT Q1 is lower than the voltage of the emitter of the pnp BJT Q1, then the pnp BJT Q1 is turned on accordingly. The collector of the pnp BJT Q1 is electronically connected to the voltage port V3.3 via the pnp BJT, which is turned on and at a high voltage. The detection pin 301 of the processing unit 30 then obtains the high voltage signal. The processing unit 30 then controls to display the remaining power of the battery when receiving the high voltage signal.
In the embodiment, the electronic device 100 can be a mobile phone, a digital camera, a digital photo frame, an electronic reader, for example.
It is believed that the present embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the disclosure or sacrificing all of its material advantages, the examples hereinbefore described merely being exemplary embodiments of the present disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201210095713.1 | Apr 2012 | CN | national |
